The evidence texinwien points to indicates that blur due to SS can occur even when shooting from a tripod. It does not demonstrate that the risk of blur due to SS increases when shooting from a tripod.

In my own quite extensive testing with my E-M5, it is clearly the other way around. The risk/magnitude of blur due to SS declines when shooting from a tripod. Furthermore, when using a sufficiently heavy and sturdy "tripod" (such as the floor of my kitchen with tiles on top of conrete), there is no blur at all due to SS even with my 100-300 at 300 mm and no anti-shock delay.

The reason why a tripod can decrease the risk of blur due to SS is that one important mechanism (and the only one I have so far found clear-cut evidence for in the tests I have conducted with my own gear although I remain open to other possibilities) is that shutter action causes a displacement of the camera as a whole. The risk/magnitude of such displacement declines if the camera is put on a reasonably sturdy tripod and is eliminated altogether if it is put on a sufficently heavy and sturdy "tripod" of the type described above. In other words, given that SS causes blur via displacement of the camera as a whole, the risk/magnitude of such blur declines if the camera "has no place to go".

No, it effectively prevents it from going upwards too due to the behavior of the normal force (the one counteracting the force of gravity) on a rigid as opposed to a non-rigid surface.

Sorry, but don't quite understand what it is that should prevent the camera from moving upwards/sidewards. My electric shaver will still vibrate if put on hard/heavy surface. Probably less than if put on a carpet, but still.

The camera may still vibrate (relative internal displacements) but it will not be displaced as a whole. Consider, for example, what will happen when the shutter blades accelerate downwards. According to Newton's third law (that of action and reaction), the force accelerating the blades implies that an equally large force is acting on the camera as a whole (apart from the shutter blades) in the opposite direction (upwards). This effectively reduces the downward force of gravity on the camera.

If the camera is sitting on a perfectly rigid surface, the normal force (the one acting upwards, counteracting the force of gravity) will instantly adapt so as to match the reduced downward force. The camera will therefore not move at all. If, instead, the camera is sitting in the soft flesh of your hands, it is effectively sitting on a spring-loaded mechanism. In this case, the normal force cannot be reduced except by having the depressed flesh expand a bit. Consequently, the camera will move upwards until the expansion is sufficient to reach partiy between downward and upward forces.

Yes, understand that, but if the opward force is large enough to overcome the force of gravity, then the camera will move upwards (we're talking microns here), and sidewards if large enough to overcome (just) the friction. That's the case with my electric shaver. The forces/vibrations are strong enough to move it around on a hard floor. A hard/heavy surface certainly helps, but don't think it's impossible that e.g. an E-M1 in burst mode would move a bit around too (it's my impression that the E-M1 has a more 'violent' shutter than the E-M5).

The upward force created by shutter acceleration is nowhere nearly enough to outdo the downward force of gravity.

Hmm.. won't a force (in this case a sudden/tempotary force) always have an effect, no matter how small it is? A small force will have a small effect, like maybe a 1 micron movement upwards, and a larger force will have a larger effect, like 10 micron movement, before gravity again takes over.

The way to work this out is to calculate the net force - i.e. add the force of gravity (camera mass X 1g down) to the varying instantaneous force (up and down). If the net force ever crosses zero, the camera jumps in the air. That's how it works.

Ken

What you are describing with your shaver is the impact of vibration (relative internal displacement) and this can of course move an object around if sufficiently strong.

But that's not what I was talking about and the reason for conducting my on-the-floor test was precisely to separate vibration from displacement of the whole camera due to forces of the kind described above. Putting the camera on the floor prevents the latter but not the former. The results of my test showed the latter to be the culprit since there was no blur with the camera on the floor although there was when using an ordinary tripod (with my 100-300 at 300). The same result was obtained in this test with a Pentax K-7 (see section 4.2, finding #6).

Of course, that doesn't preclude the possibility that other results might be obtained with other gear (including other specimen of the same gear).

Interestingly, vibrations can be used productively for photography, as exemplified by this panorma app for iPhone 5, which uses the vibration function of the phone to move it around for a panorma sweep.